A sphere theorem on locally conformally flat even-dimensional manifolds

In this paper, we prove that a closed even-dimensional manifold which is locally conformally flat with positive scalar curvature, positive Euler characteristic and which satisfies some additional condition on its curvature is diffeomorphic to the sphere or projective space.     

Higher moments of the waiting time distribution in M/G/1 retrial queues

This work analyzes the waiting time distribution in the M/G/1 retrial queue. The first two moments of the waiting time distribution are known from the literature. In this work we obtain all the moments of the waiting time distribution.     

Phase equilibrium data and thermodynamic modelling of the system (propane + DMF + methanol) at high pressures

Reported in this work are phase equilibrium data at high pressures for the binary and ternary systems formed by {propane + N,N-dimethylformamide (DMF) + methanol}. Phase equilibrium measurements were performed in a high-pressure, variable-volume view cell, following the static synthetic method for obtaining the experimental bubble and dew points transition data over the temperature range of (363 to 393) K, pressures up to 11.5 MPa and overall mole fraction of the lighter component varying from 0.1 to 0.995. For the systems investigated, vapour–liquid (VLE), liquid–liquid (LLE) and vapour–liquid–liquid (VLLE) phase transitions were visually recorded. Results show that the systems investigated present UCST (upper critical solution temperature) phase transition curves with an UCEP (upper critical end point) at a temperature higher than the propane critical temperature. The experimental data were modelled using the Peng–Robinson equation of state with the Wong–Sandler and the classical quadratic mixing rules, affording a satisfactory representation of the experimental data.     

Controlling the Stepwise Closing of Identical DTE Photochromic Units with Electrochemical and Optical Stimuli

The full or stepwise controlled closing of identical photochromic dithienylethene units in the same molecule was addressed with a combination of electrochemical and optical stimuli in a trimetallic carbon-rich ruthenium complex.     

Voltammetric determination of Rutin at Screen-Printed carbon disposable electrodes

Rutin is a flavonoid commonly employed for many therapeutic purposes. Although the electroactive phenolic groups of rutin might be oxidized at low applied potential, the adsorption of oxidized species changes the electrode surface. As a consequence, the repeatability and reproducibility of the method decreases, which limits electroanalytical applications. This paper describes the use of disposable screen-printed electrodes as an alternative to improve the electrochemical quantification of rutin in commercial and standard samples. The electrochemical behavior was consistent to what is observed using other carbon electrodes: an adsorption-involved step and a pH-dependent oxidation process. The replacement of the electrodes between the analyses ensured rapid analysis, good intermediate precision and repeatability. The proposed method was successfully applied to rutin determination in pharmaceutical samples of capsules, with the limit of quantification being 0.30 μM.      

Single-crystal EPR study and DFT structure of the [Mo(CO)5PPh3]+· radical cation

A radical species characterized by a large g-anisotropy and a clearly resolved hyperfine structure with ^95/97Mo and ³¹P nuclei is formed, at 77 K, by radiolysis of a single crystal of Mo(CO)₅PPh₃. The corresponding EPR signals disappear irreversibly with increasing temperature and the angular dependence of the various coupling constants imply a spin delocalization of ～60% and ～4% on the molybdenum and the phosphorus atoms, respectively and are, a priori, consistent with the trapping of a one-electron deficient centre. The ability of DFT to predict the EPR tensors for a 17-electron Mo^(I) species is verified by calculating the g-tensor and the various ¹⁴N and ¹³C coupling tensors previously reported by Hayes for [Mo(CN)₅NO]^3?. Calculations at the B3LYP/ZORA/SOMF level of theory show that, in contrast to Mo(CO)₅PH₃, one-electron oxidation of Mo(CO)₅PPh₃ causes an appreciable change in the geometry of the complex. The g-tensor and the ^95/97Mo and ³¹P isotropic and anisotropic coupling constants calculated for [Mo(CO)₅PPh₃]^+· confirm the trapping of this species in the irradiated crystal of Mo(CO)₅PPh₃; they also show that the conformational modifications induced by the electron release are probably hindered by the nearby complexes.     

Phase behaviour of heavy petroleum fractions in pure propane and n-butane and with methanol as co-solvent

This work reports phase equilibrium experimental results for heavy petroleum fractions in pure propane and n-butane as primary solvents and using methanol as co-solvent. Three kinds of oils were investigated from Marlim petroleum: a relatively light fraction coming from the first distillation of crude petroleum at atmospheric pressure (GOP – heavy gas oil of petroleum), the residue of such distillation (RAT) and the crude petroleum sample. Phase equilibrium measurements were performed in a high-pressure, variable-volume view cell, following the static synthetic method, over the temperature range of 323 K to 393 K, pressures up to 10 MPa and overall compositions of heavy component varying from 1 wt% to 40 wt%. Transition pressures for low methanol and oil concentrations were very close for GOP, RAT, and crude Marlim when using propane as the primary solvent. Close to propane critical temperature, two and three-phase transitions were observed for GOP and Marlim when methanol was increased. When n-butane was used as primary solvent, all transitions observed were of (vapour + liquid) type with transition pressure values smaller than those obtained for propane.     

High-pressure optical studies on R-line fluorescence lifetime in Al2O3:V2+

The effect of high hydrostatic pressure (up to 10.3?GPa) at room temperature on fluorescence lifetime τ for R line (²E→⁴A₂ transition) in ruby Al₂O₃:V²⁺ was studied. The performed studies show the linear increase of τ with increasing pressure. At 10.3?GPa, τ is about 1.36 times higher than at ambient pressure. The obtained trend was explained by a model which considered the effect of pressure on τ through an induced change of line position, inter-ionic distance, compressibility, and molecular polarizability. A good agreement between the calculated and experimental values for τ was obtained.     

Polymerized Lyotropic Liquid Crystal Assemblies for Membrane Applications

Cross‐linked lyotropic liquid crystal (LLC) assemblies represent a new class of polymer materials for membrane applications. These materials are formed by the phase‐segregation and self‐assembly of polymerizable amphiphiles in water into condensed ordered ensembles that can be cross‐linked in situ with retention of microstructure. The resulting LLC polymer networks have ordered, nanometer‐scale aqueous and cross‐linked organic domains, which can be used to affect gas solubility and diffusivity through the polymer to help separate molecules via the solution–diffusion mechanism. The open aqueous domains can also be used for pore transport and size exclusion with resolution on the molecular size level. The use and application potential of cross‐linked LLC assemblies as gas separation membranes, selective vapor barrier materials, and water nanofiltration and desalination membranes are presented.